<TITLE>Editable Postscript Interchange Format</TITLE>
<H1>IPF</H1>
<XMP>
Date: Sun, 6 Oct 91 14:14:18 PDT
From: kehoe@fortuity.sf.ca.us (Daniel Miles Kehoe)
To: timbl@nxoc01.cern.ch (Tim Berners-Lee)
Subject: Interchange PostScript Format

Tim,

I'm sending you the complete text of an article from the Seybold Report on Desktop Publishing. I believe you'll find it very interesting. Incidentally, it is copied without permission.

Regards,
Daniel Kehoe

P.S. Any new developments with WWW?

</XMP>[Note this is copyright material: Subscribe to the Seybold report
rather than print this! -Tim]
<H1>Adobe unveils editable PostScript interchange format</H1>Combines Multiple Master fonts, Illustrator 3.O file format, viewer<P>
Adobe Systems announced that it has developed a PostScript-based technol-
ogy for exchanging formatted elec- tronic documents. Adobe's approach
to this problem draws on several existing technologies, including
the Illustrator file format, Multiple Master fonts and a newly announced
font rasterizing chip. However, Adobe is not announcing any specific
product at this time.<P>
When Adobe's vision is fully fleshed out with deliverable products,
it promises to let you move documents freely around a network, viewing
them on a wide range of computer platforms. Although these documents
will be in final form and ready for presentation, they will continue
to be editable.<P>
As John Warnock was expected to sketch out in a speech to the Seybold
Computer Publishing Conference this week, much of the software needed
to do this already exists. The remaining problems are partly legal
and licensing issues, and partly a continuing process of developing
standards.
<H2>The IPF</H2>At the heart of Adobe's approach is the Interchange PostScript Format.
This is based on the current Illustrator 3.0 file format, which is
a subset of the PostScript language. The existence of Illustrator
demonstrates that it is possible to have a file format capable of
describing and outputting complex pages without losing the abil- ity
to edit those pages. You can think of Illustrator as a complex editing
pro- gram whose native file format expresses the exact appearance
of a document.<P>
Illustrator 3.0 does not handle all document types, of course. It
knows nothing of multipage documents, style sheets, reference constructs
or scanned images. In IPF (and presumably in fu- ture Illustrator-like
products), Adobe clearly intends to extend the range of objects to
cope with these needs.
<H2>Platform independent</H2>A major Adobe goal is that the author or reader of a document should
not have to care what kind of computer other readers or editors usc.
That is, IPF needs to be independent of any particular display, central
processor or operating system.<P>
This is relatively straightforward; PostScript was from the beginning
de- signed to be device independent. At the Seybold Conference, Warnock
was expected to demonstrate the new tech- nology on a Mac, PCs running
DOS and Windows, and a Unix workstation.
<H2>Font woes</H2>If a remote viewer is to read a formatted text document you have just
created, it needs to have the same fonts you do, right? And since
it probably doesn't have all of your fonts, you either must restrict
yourself to using least-common-denominator fonts or send the fonts
along with the docu- ment. That, in turn, swells the size of the file
and raises the hackles of the font vendors. It probably also gives
your corporate counsel an ulcer just thinking about the potential
copyright- infringement lawsuits.<P>
 Adobe's solution here is two- pronged. First, Adobe says, all you
need to send is the font metrics--the character widths and kerning
tables. At the receiving end, a document viewer program can use Multiple
Master fonts to generate good-looking type that ex- actly matches
the formatting of the original text. In fact, Adobe claims that for
most normal text faces, the on- screen appearance of the synthesized
fonts will be indistinguishable from the original fonts.<P>
However, there is a fall-back approach: send the fonts. Adobe is work-
ing with other major font vendors to modify the shrink-wrap font license
to permit distribution for read-only or print-only use. Adobe will
license this use for its own fonts, and the ITC (the licensing agency
for a substantial fraction of everybody's font libraries) has agreed
to do so as well. The other font houses will probably go along sooner
or later.<P>
(A third method--sending along the name of the font and its metrics-
depends on a standardized naming scheme and presumes font-substitution
smarts by a viewer at the other end. This method is being considered
for ISO interchange formats.)
<H2>New PostScript drivers </H2>A true interchange solution must work for all document-creation programs:
word processors, spreadsheets, CAD and illus- tration packages, database
report genera- tors and so on. Just about all of these products can
print to a PostScript de- vice, and they usually go through the system
printer driver.<P>
Adobe announced last winter that it would be developing the PostScript
drivers for future Apple and Windows operating systems. So it will
simply add to its drivers the ability to generate an IPF file. At
that point, every existing application will be able to create inter-
change-ready documents.<P>
There is an installed base of older applications that generate their
own PostScript code and so will not benefit from Adobe's new device
drivers. A program that converts the full range of PostScript into
the more restrictive IPF would be tantamount to a complete PostScript
interpreter. This is exactly how Adobe plans to assure backward compatibility.<P>
However, Adobe points out that you wouldn't need this interpreter
in every workstation. You could run it as a task at one station on
the network-- in the mail server, for example.
<H2>Viewer apps </H2>The final part of Adobe's strategy is to develop viewer applications
to display and print IPF documents. There might also be appli- cations
that can annotate or edit these files. Clearly, these programs will
be specific to a particular processor and operating system. Each user
interface will have to be separately developed. However, a great deal
of the code can be shared across platforms.<P>
Adobe has not given any hints about when such viewers might be released.
However, the core code has already been written and demonstrated,
so we don't expect to wait years. We might hope for an announcement
next spring; but Adobe has politely declined to speculate on that
subject.
<H2>ATM on a chip</H2>Among the products Adobe is announcing this week is a Type 1 font
rendering chip that can rasterize 2,000 roman characters per second.
No end-user products using this chip exist yet. But like Destiny Technology's
RIDA chip (see p. 40), it could be used in graphics boards, print-
ers or computer motherboards.<P>
Adobe says that text rendering is so fast with its new "ATM chip"
that you can continuously zoom a page with no perceptible jerkiness--new
full- page bitmaps can be generated at speeds comparable with the
monitor's frame rate. This kind of hardware accel- eration will clearly
be vital in gaining consumer acceptance of PostScript for viewing
documents.
<H2>Capturing the semantics</H2>Post-Script, as it stands, can only describe the appearance of a page;
it can express all the QuickDraw or Windows GDI information, but it
cannot show the relationships of objects (the formulas in a spreadsheet
or the element groupings of a CAD drawing, for example). IPF can be
extended to express object se- mantics. However, this partly depends
on extending the application programs themselves to support document
inter- change, and so it will be an evolution- ary process.
<H2>Prospects</H2>Adobe is in a better position than any other vendor to promulgate
a document interchange format. It is a tireless champion of PostScript-
based solutions, and it is better positioned to deliver products to
the mass market on multiple platforms than any of the platform vendors.
(DEC, IBM, Microsoft and Apple all have some stake in developing interchange
formats.) Aside from formats from these vendors, the only other document
interchange format is the Document Style Semantics and Specification
Language (DSSSL), a draft international standard that is still too
new to have any products using it yet. Although DSSSL is comprehensive,
it has no vendor with a financial stake in its success to champion
its cause. It is also very complex, so it may never have an implementation
in mass-market products.<P>
Adobe's format will be implemented immediately by Adobe, and its status
as a "standard" could change if it meets with popular acceptance.
(After all, PostScript has become an ISO standard.) Everything depends
on how well Adobe's implementations meet users' requirements for electronic
document interchange.
<ADDRESS>Seybold Report on Desktop Publishing; October 2, 1991</A>
</ADDRESS>